1. Field of the Invention
The present invention relates to inhibitors of the nucleic enzyme poly(adenosine 5xe2x80x2-diphospho-ribose)polymerase [xe2x80x9cpoly(ADP-ribose)polymerasexe2x80x9d or xe2x80x9cPARPxe2x80x9d, which is also sometimes called xe2x80x9cPARSxe2x80x9d for poly(ADP-ribose)synthetase or xe2x80x9cPARTxe2x80x9d for poly(ADP-ribose)transferase]. More particularly, the invention relates to the use of PARP inhibitors to prevent and/or treat tissue damage resulting from cell damage or death due to necrosis or apoptosis, neural tissue damage resulting from ischemia and reperfusion injury, neurological disorders and neurodegenerative diseases; to prevent or treat vascular stroke; to treat or prevent cardiovascular disorders; to treat other conditions and/or disorders such as age-related macular degeneration, AIDS and other immune diseases, arthritis, atherosclerosis, cachexia, cancer, degenerative diseases of skeletal muscle involving replicative senescence, diabetes, head trauma, immune senescence, inflammatory bowel disorders (such as colitis and Crohn""s disease), muscular dystrophy, osteoarthritis, osteoporosis, chronic and acute pain (such as neuropathic pain), renal failure, retinal ischemia, septic shock (such as endotoxic shock), and skin aging; to extend the lifespan and proliferative capacity of cells; to alter gene expression of senescent cells; or to radiosensitize hypoxic tumor cells.
2. Description of the Prior Art
Poly(ADP-ribose)polymerase (xe2x80x9cPARPxe2x80x9d) is a type of enzyme located in the nuclei of cells of various organs, including muscle, heart and brain cells. Several structural variants or isoforms of PARP enzymes have been isolated in various species and tissue types, and all of these enzymes are capable of PARP activity which consists of ADP-ribosylation. Babiychuk et al., xe2x80x9cHigher Plants Possess Two Structurally Different Poly(ADP-Ribose)Polymerasesxe2x80x9d, (1998) Plant Journal 15:635-645. Smith et al., xe2x80x9cTankyrase, a Poly(ADP-Ribose)Polymerase at Human Telomeresxe2x80x9d, Science 282:1484-1487 (1998). These structurally-variant forms of PARP enzymes are all referred to herein as PARP. Furthermore, the compounds of the present invention would be expected to inhibit the PARP activity of any and all enzymes which can perform ADP-Ribosylation. These PARP enzymes, collectively referred to as PARP, play a physiological role in the repair of strand breaks in DNA. Once activated by damaged DNA fragments, PARP catalyzes the attachment of up to 100 ADP-ribose units to a variety of nuclear proteins, including histones and PARP itself. While the exact range of functions of PARP has not been fully established, this enzyme is thought to play a role in enhancing DNA repair.
During major cellular stresses, however, the extensive activation of PARP can rapidly lead to cell damage or death through depletion of energy stores. Four molecules of ATP are consumed for every molecule of NAD (the source of ADP-ribose) regenerated. Thus, NAD, the substrate of PARP, is depleted by massive PARP activation and, in the efforts to re-synthesize NAD, ATP may also be depleted.
It has been reported that PARP activation plays a key role in both glutamate- and NO-induced neurotoxicity, as shown by the use of PARP inhibitors to prevent such toxicity in cortical cultures in proportion to their potencies as inhibitors of this enzyme (Zhang et al., xe2x80x9cNitric Oxide Activation of Poly(ADP-Ribose)Synthetase in Neurotoxicityxe2x80x9d, Science, 263:687-89 (1994)); and in hippocampal slices (Wallis et al., xe2x80x9cNeuroprotection Against Nitric Oxide Injury with Inhibitors of ADP-Ribosylationxe2x80x9d, NeuroReport, 5:3, 245-48 (1993)). The potential role of PARP inhibitors in treating neurodegenerative diseases and head trauma has thus been known. Research, however, continues to pinpoint the exact mechanisms of their salutary effect in cerebral ischemia, (Endres et al., xe2x80x9cIschemic Brain Injury is Mediated by the Activation of Poly(ADP-Ribose)Polymerasexe2x80x9d, J. Cereb. Blood Flow Metabol., 17:1143-51 (1997)) and in traumatic brain injury (Wallis et al., xe2x80x9cTraumatic Neuroprotection with Inhibitors of Nitric Oxide and ADP-Ribosylation, Brain Res., 710:169-77 (1996)).
It has been demonstrated that single injections of PARP inhibitors have reduced the infarct size caused by ischemia and reperfusion of the heart or skeletal muscle in rabbits. In these studies, a single injection of the PARP inhibitor, 3-amino-benzamide (10 mg/kg), either one minute before occlusion or one minute before reperfusion, caused similar reductions in infarct size in the heart (32-42%). Another PARP inhibitor, 1,5-dihydroxyisoquinoline (1 mg/kg), reduced infarct size by a comparable degree (38-48%). Thiemermann et al., xe2x80x9cInhibition of the Activity of Poly(ADP Ribose)Synthetase Reduces Ischemia-Reperfusion Injury in the Heart and Skeletal Musclexe2x80x9d, Proc. Natl. Acad. Sci. USA, 94:679-83 (1997). This finding has suggested that PARP inhibitors might be able to salvage previously ischemic heart or skeletal muscle tissue.
PARP activation has also been shown to provide an index of damage following neurotoxic insults by glutamate (via NMDA receptor stimulation), reactive oxygen intermediates, amyloid xcex2-protein, n-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and its active metabolite N-methyl-4-phenylpyridine (MPP+), which participate in pathological conditions such as stroke, Alzheimer""s disease and Parkinson""s disease. Zhang et al., xe2x80x9cPoly(ADP-Ribose)Synthetase Activation: An Early Indicator of Neurotoxic DNA Damagexe2x80x9d, J. Neurochem., 65:3, 1411-14 (1995). Other studies have continued to explore the role of PARP activation in cerebellar granule cells in vitro and in MPTP neurotoxicity. Cosi et al., xe2x80x9cPoly(ADP-Ribose)Polymerase (PARP) Revisited. A New Role for an Old Enzyme: PARP Involvement in Neurodegeneration and PARP Inhibitors as Possible Neuroprotective Agentsxe2x80x9d, Ann. N.Y. Acad. Sci., 825:366-79 (1997); and Cosi et al., xe2x80x9cPoly(ADP-Ribose)Polymerase Inhibitors Protect Against MPTP-induced Depletions of Striatal Dopamine and Cortical Noradrenaline in C57B1/6 Micexe2x80x9d, Brain Res., 729:264-69 (1996).
Neural damage following stroke and other neurodegenerative processes is thought to result from a massive release of the excitatory neurotransmitter glutamate, which acts upon the N-methyl-D-aspartate (NMDA) receptors and other subtype receptors. Glutamate serves as the predominate excitatory neurotransmitter in the central nervous system (CNS). Neurons release glutamate in great quantities when they are deprived of oxygen, as may occur during an ischemic brain insult such as a stroke or heart attack. This excess release of glutamate in turn causes over-stimulation (excitotoxicity) of N-methyl-D-aspartate (NMDA), AMPA, Kainate and MGR receptors. When glutamate binds to these receptors, ion channels in the receptors open, permitting flows of ions across their cell membranes, e.g., Ca2+ and Na+ into the cells and K+ out of the cells. These flows of ions, especially the influx of Ca2+, cause overstimulation of the neurons. The over-stimulated neurons secrete more glutamate, creating a feedback loop or domino effect which ultimately results in cell damage or death via the production of proteases, lipases and free radicals. Excessive activation of glutamate receptors has been implicated in various neurological diseases and conditions including epilepsy, stroke, Alzheimer""s disease, Parkinson""s disease, Amyotrophic Lateral Sclerosis (ALS), Huntington""s disease, schizophrenia, chronic pain, ischemia and neuronal loss following hypoxia, hypoglycemia, ischemia, trauma, and nervous insult. Recent studies have also advanced a glutamatergic basis for compulsive disorders, particularly drug dependence. Evidence includes findings in many animal species, as well as, in cerebral cortical cultures treated with glutamate or NMDA, that glutamate receptor antagonists block neural damage following vascular stroke. Dawson et al., xe2x80x9cProtection of the Brain from Ischemiaxe2x80x9d, Cerebrovascular Disease, 319-25 (H. Hunt Batjer ed., 1997). Attempts to prevent excitotoxicity by blocking NMDA, AMPA, Kainate and MGR receptors have proven difficult because each receptor has multiple sites to which glutamate may bind. Many of the compositions that are effective in blocking the receptors are also toxic to animals. As such, there is no known effective treatment for glutamate abnormalities.
The stimulation of NMDA receptors, in turn, activates the enzyme neuronal nitric oxide synthase (NNOS), which causes the formation of nitric oxide (NO), which more directly mediates neurotoxicity. Protection against glutamate neurotoxicity mediated through the NMDA receptors has occurred following treatment with NOS inhibitors. See Dawson et al., xe2x80x9cNitric Oxide Mediates Glutamate Neurotoxicity in Primary Cortical Culturesxe2x80x9d, Proc. Natl. Acad. Sci. USA, 88:6368-71 (1991); and Dawson et al., xe2x80x9cMechanisms of Nitric Oxide-mediated Neurotoxicity in Primary Brain Culturesxe2x80x9d, J. Neurosci., 13:6, 2651-61 (1993). Protection against glutamate neurotoxicity mediated through NMDA receptors can also occur in cortical cultures from mice with targeted disruption of NNOS. See Dawson et al., xe2x80x9cResistance to Neurotoxicity in Cortical Cultures from Neuronal Nitric Oxide Synthase-Deficient Micexe2x80x9d, J. Neurosci., 16:8, 2479-87 (1996).
It is known that neural damage following vascular stroke is markedly diminished in animals treated with NOS inhibitors or in mice with NNOS gene disruption. Iadecola, xe2x80x9cBright and Dark Sides of Nitric Oxide in Ischemic Brain Injuryxe2x80x9d, Trends Neurosci., 20:3, 132-39 (1997); and Huang et al., xe2x80x9cEffects of Cerebral Ischemia in Mice Deficient in Neuronal Nitric Oxide Synthasexe2x80x9d, Science, 265:1883-85 (1994). See also, Beckman et al., xe2x80x9cPathological Implications of Nitric Oxide, Superoxide and Peroxynitrite Formationxe2x80x9d, Biochem. Soc. Trans., 21:330-34 (1993). Either NO or peroxynitrite can cause DNA damage, which activates PARP. Further support for this is provided in Szabxc3x3 et al., xe2x80x9cDNA Strand Breakage, Activation of Poly(ADP-Ribose)Synthetase, and Cellular Energy Depletion are Involved in the Cytotoxicity in Macrophages and Smooth Muscle Cells Exposed to Peroxynitritexe2x80x9d, Proc. Natl. Acad. Sci. USA, 93:1753-58 (1996).
Zhang et al., U.S. Pat. No. 5,587,384 issued Dec. 24, 1996, discusses the use of certain PARP inhibitors, such as benzamide and 1,5-dihydroxy-isoquinoline, to prevent NMDA-mediated neurotoxicity and, thus, treat stroke, Alzheimer""s disease, Parkinson""s disease and Huntington""s disease. However, it is has now been discovered that Zhang et al. may have been in error in classifying neurotoxicity as NMDA-mediated neurotoxicity. Rather, the in vivo neurotoxicity present is more appropriately classified as glutamate neurotoxicity. See Zhang et al. xe2x80x9cNitric Oxide Activation of Poly(ADP-Ribose)Synthetase in Neurotoxicityxe2x80x9d, Science, 263:687-89 (1994). See also, Cosi et al., Poly(ADP-Ribose)Polymerase Inhibitors Protect Against MPTP-induced Depletions of Striatal Dopamine and Cortical Noradrenaline in C57B1/6 Micexe2x80x9d, Brain Res., 729:264-69 (1996).
It is also known that PARP inhibitors affect DNA repair generally. Cristovao et al., xe2x80x9cEffect of a Poly(ADP-Ribose)Polymerase Inhibitor on DNA Breakage and Cytotoxicity Induced by Hydrogen Peroxide and xcex3-Radiation,xe2x80x9d Terato., Carcino., and Muta., 16:219-27 (1996), discusses the effect of hydrogen peroxide and xcex3-radiation on DNA strand breaks in the presence of and in the absence of 3-aminobenzamide, a potent inhibitor of PARP. Cristovao et al. observed a PARP-dependent recovery of DNA strand breaks in leukocytes treated with hydrogen peroxide.
PARP inhibitors have been reported to be effective in radiosensitizing hypoxic tumor cells and effective in preventing tumor cells from recovering from potentially lethal damage of DNA after radiation therapy, presumably by their ability to prevent DNA repair. See U.S. Pat. Nos. 5,032,617; 5,215,738; and 5,041,653.
Evidence also exists that PARP inhibitors are useful for treating inflammatory bowel disorders. Salzman et al., xe2x80x9cRole of Peroxynitrite and Poly(ADP-Ribose)Synthase Activation Experimental Colitis,xe2x80x9d Japanese J. Pharm., 75, Supp. I:15 (1997), discusses the ability of PARP inhibitors to prevent or treat colitis. Colitis was induced in rats by intraluminal administration of the hapten trinitrobenzene sulfonic acid in 50% ethanol and treated with 3-aminobenzamide, a specific inhibitor of PARP activity. Inhibition of PARP activity reduced the inflammatory response and restored the morphology and the energetic status of the distal colon. See also, Southan et al., xe2x80x9cSpontaneous Rearrangement of Amino-alkylithioureas into Mercaptoalkylguanidines, a Novel Class of Nitric Oxide Synthase Inhibitors with Selectivity Towards the Inducible Isoformxe2x80x9d, Br. J. Pharm., 117:619-32 (1996); and Szabxc3x3 et al., xe2x80x9cMercaptoethylguanidine and Guanidine Inhibitors of Nitric Oxide Synthase React with Peroxynitrite and Protect Against Peroxynitrite-induced Oxidative Damagexe2x80x9d, J. Biol. Chem., 272:9030-36 (1997).
Evidence also exists that PARP inhibitors are useful for treating arthritis. Szabxc3x3 et al., xe2x80x9cProtective Effects of an Inhibitor of Poly(ADP-Ribose)Synthetase in Collagen-Induced Arthritis,xe2x80x9d Japanese J. Pharm., 75, Supp. I:102 (1997), discusses the ability of PARP inhibitors to prevent or treat collagen-induced arthritis. See also Szabxc3x3 et al., xe2x80x9cDNA Strand Breakage, Activation of Poly(ADP-Ribose)Synthetase, and Cellular Energy Depletion are Involved in the Cytotoxicity in Macrophages and Smooth Muscle Cells Exposed to Peroxynitrite,xe2x80x9d Proc. Natl. Acad. Sci. USA, 93:1753-58 (March 1996); Bauer et al., xe2x80x9cModification of Growth Related Enzymatic Pathways and Apparent Loss of Tumorigenicity of a ras-transformed Bovine Endothelial Cell Line by Treatment with 5-Iodo-6-amino-1,2-benzopyrone (INH2BP)xe2x80x9d, Intl. J. Oncol., 8:239-52 (1996); and Hughes et al., xe2x80x9cInduction of T Helper Cell Hyporesponsiveness in an Experimental Model of Autoimmunity by Using Nonmitogenic Anti-CD3 Monoclonal Antibodyxe2x80x9d, J. Immuno., 153:3319-25 (1994).
Further, PARP inhibitors appear to be useful for treating diabetes. Heller et al., xe2x80x9cInactivation of the Poly(ADP-Ribose)Polymerase Gene Affects Oxygen Radical and Nitric Oxide Toxicity in Islet Cells,xe2x80x9d J. Biol. Chem., 270:19, 11176-80 (May 1995), discusses the tendency of PARP to deplete cellular NAD+ and induce the death of insulin-producing islet cells. Heller et al. used cells from mice with inactivated PARP genes and found that these mutant cells did not show NAD+ depletion after exposure to DNA-damaging radicals. The mutant cells were also found to be more resistant to the toxicity of NO.
Further still, PARP inhibitors have been shown to be useful for treating endotoxic shock or septic shock. Zingarelli et al., xe2x80x9cProtective Effects of Nicotinamide Against Nitric Oxide-Mediated Delayed Vascular Failure in Endotoxic Shock: Potential Involvement of PolyADP Ribosyl Synthetase,xe2x80x9d Shock, 5:258-64 (1996), suggests that inhibition of the DNA repair cycle triggered by poly(ADP ribose)synthetase has protective effects against vascular failure in endotoxic shock. Zingarelli et al. found that nicotinamide protects against delayed, NO-mediated vascular failure in endotoxic shock. Zingarelli et al. also found that the actions of nicotinamide may be related to inhibition of the NO-mediated activation of the energy-consuming DNA repair cycle, triggered by poly(ADP ribose)synthetase. See also, Cuzzocrea, xe2x80x9cRole of Peroxynitrite and Activation of Poly(ADP-Ribose)Synthetase in the Vascular Failure Induced by Zymosan-activated Plasma,xe2x80x9d Brit. J. Pharm., 122:493-503 (1997).
Yet another known use for PARP inhibitors is treating cancer. Suto et al., xe2x80x9cDihydroisoquinolinones: The Design and Synthesis of a New Series of Potent Inhibitors of Poly(ADP-Ribose)Polymerasexe2x80x9d, Anticancer Drug Des., 7:107-17 (1991), discloses processes for synthesizing a number of different PARP inhibitors. In addition, Suto et al., U.S. Pat. No. 5,177,075, discusses several isoquinolines used for enhancing the lethal effects of ionizing radiation or chemotherapeutic agents on tumor cells. Weltin et al., xe2x80x9cEffect of 6(5H)-Phenanthridinone, an Inhibitor of Poly(ADP-ribose)Polymerase, on Cultured Tumor Cellsxe2x80x9d, Oncol. Res., 6:9, 399-403 (1994), discusses the inhibition of PARP activity, reduced proliferation of tumor cells, and a marked synergistic effect when tumor cells are co-treated with an alkylating drug.
Still another use for PARP inhibitors is the treatment of peripheral nerve injuries, and the resultant pathological pain syndrome known as neuropathic pain, such as that induced by chronic constriction injury (CCI) of the common sciatic nerve and in which transsynaptic alteration of spinal cord dorsal horn characterized by hyperchromatosis of cytoplasm and nucleoplasm (so-called xe2x80x9cdarkxe2x80x9d neurons) occurs. See Mao et al., Pain, 72:355-366 (1997).
PARP inhibitors have also been used to extend the lifespan and proliferative capacity of cells including treatment of diseases such as skin aging, Alzheimer""s disease, atherosclerosis, osteoarthritis, osteoporosis, muscular dystrophy, degenerative diseases of skeletal muscle involving replicative senescence, age-related macular degeneration, immune senescence, AIDS, and other immune diseases; and to alter gene expression of senescent cells. See WO 98/27975.
Large numbers of known PARP inhibitors have been described in Banasik et al., xe2x80x9cSpecific Inhibitors of Poly(ADP-Ribose)Synthetase and Mono(ADP-Ribosyl)-Transferasexe2x80x9d, J. Biol. Chem., 267:3, 1569-75 (1992), and in Banasik et al., xe2x80x9cInhibitors and Activators of ADP-Ribosylation Reactionsxe2x80x9d, Molec. Cell. Biochem., 138:185-97 (1994).
However, the approach of using these PARP inhibitors in the ways discussed above has been limited in effect. For example, side effects have been observed with some of the best-known PARP inhibitors, as discussed in Milam et al., xe2x80x9cInhibitors of Poly(Adenosine Diphosphate-Ribose)Synthesis: Effect on Other Metabolic Processesxe2x80x9d, Science, 223:589-91 (1984). Specifically, the PARP inhibitors 3-aminobenzamide and benzamide not only inhibited the action of PARP but also were shown to affect cell viability, glucose metabolism, and DNA synthesis. Thus, it was concluded that the usefulness of these PARP inhibitors may be severely restricted by the difficulty of finding a dose that will inhibit the enzyme without producing additional metabolic effects.
The inventors have now discovered that selected phenazine compounds can inhibit PARP activity. These compounds and can treat or prevent tissue damage resulting from cell damage or death due to necrosis or apoptosis and/or can ameliorate neural tissue damage, including that following focal ischemia and reperfusion injury.
Accordingly, there remains a need for novel PARP inhibitors, and compositions containing the same, and methods for using the same. Particularly there remains a need for PARP inhibitors exhibiting more potent and reliable effects with respect to treatment of tissue damage resulting from cell death or damage due to necrosis or apoptosis than know in the prior art and exhibiting less side effects.
The present invention relates to novel poly(ADP-ribose)polymerase (xe2x80x9cPARPxe2x80x9d) inhibitors, compositions containing the same, and methods for using the same.
Specifically, the present invention relates to a compound of formula I: 
wherein R1-R9 and Z are independently hydrogen, hydroxy, halo, haloalkyl, thiocarbonyl, cyano, nitro, amino, imino, alkylamino, aminoalkyl, sulfhydryl, thioalkyl, alkylthio, sulfonyl, alkylsulfonyl, C1-C9 straight or branched chain alkyl, C2-C9 straight or branched chain alkenyl, C2-C9 straight or branched chain alkynyl, C1-C6 straight or branched chain alkoxy, C2-C6 straight or branched chain alkenoxy, C2-C6 straight or branched chain alkynoxy, aryl, carbocycle, heterocycle, aralkyl, alkylaryl, alkylaryloxy, aryloxy, aralkyloxy, aralkylsulfonyl, aralkylamino, arylamino, arylazo, arylthio, or aralkylthio; or Z is 
wherein U is C or N, and R7 and R8 are defined above; and X and Y are independently aryl, carbocycle, or heterocycle;
wherein said alkyl, alkenyl, alkynyl, imino, aryl, carbocycle, heterocycle, aralkyl, alkylaryl, alkylaryloxy, aryloxy, aralkyloxy, aralkylsulfonyl, aralkylamino, arylamino, arylazo, arylthio, aralkylthio of R1-R8, X, Y, or Z is optionally substituted with one or more substituents selected from hydroxy, halo, haloalkyl, haloalkylamide, thiocarbonyl, double-bonded oxygen to form carbonyl, carboxy, alkoxy, alkenoxy, cyano, nitro, amino, imino, amide, xe2x80x94NHCOR9 or xe2x80x94COOR9 where R9 is defined above, C1-C6 straight or branched chain alkyl, C2-C6 straight or branched chain alkenyl or alkynyl, alkylamino, aminoalkyl, sulfhydryl, thioalkyl, alkylthio, sulfonyl, aryl, aralkyl, aryloxy, arylamino, arylazo, arylthio, carbocycle, or heterocycle.
A preferred embodiment of this invention is the compound of formula I, where X is a substituted or unsubstituted phenyl.
Another preferred embodiment is where Y is an aryl substituted with at least one non-hydrogen, non-interfering substituent, more preferably where the substituent is hydroxy, amino, nitro, sulfhydryl, halo, alkylamino, carboxy, or alkoxy, and most preferably where the substituent is at the ortho position of said aryl relative to said azo group of formula I bound to said aryl. In further embodiments of the invention, Y is 1-naphthyl, (2-hydroxy)-1-naphthyl, (2-amino)-1-naphthyl, (2-sulfhydryl)-1-naphthyl, phenyl, 2-hydroxy-phenyl, 2-amino-phenyl, or 2-sulfhydryl-phenyl.
In yet another embodiment of the invention, R1-R6 are independently hydrogen, hydroxy, halo, amino, nitro, lower-alkyl, lower-alkenyl, lower-alkynyl, carboxy, alkoxy, or alkenoxy. In an alternate embodiment, R1 and R4 are each methyl, and R2, R3, R5, and R6 are each hydrogen.
In still another embodiment of the present invention, Z is aryl or aralkyl, which may be substituted in any position with at least one non-hydrogen, non-interfering substituent such as hydroxy, amino, imino, nitro, amide, urea, haloalkylamide, double-bonded oxygen to form carbonyl, sulfhydryl, halo, alkylamino, alkoxyimine, carboxy, or alkoxy.
The present invention further relates to a pharmaceutical composition comprising a pharmaceutically acceptable carrier and a compound of formula (I): 
or a pharmaceutically acceptable salt, hydrate, ester, solvate, prodrug, metabolite, stereoisomer, or mixtures thereof where R1-R9 and Z are independently hydrogen, hydroxy, halo, haloalkyl, thiocarbonyl, cyano, nitro, amino, imino, alkylamino, aminoalkyl, sulfhydryl, thioalkyl, alkylthio, sulfonyl, alkylsulfonyl, C1-C9 straight or branched chain alkyl, C2-C9 straight or branched chain alkenyl, C2-C9 straight or branched chain alkynyl, C1-C6 straight or branched chain alkoxy, C2-C6 straight or branched chain alkenoxy, C2-C6 straight or branched chain alkynoxy, aryl, carbocycle, heterocycle, aralkyl, alkylaryl, alkylaryloxy, aryloxy, aralkyloxy, aralkylsulfonyl, aralkylamino, arylamino, arylazo, arylthio, or aralkylthio; or Z is 
wherein U is C or N, and R7 and R8 are defined above; and X and Y are independently aryl, carbocycle, or heterocycle;
wherein said alkyl, alkenyl, alkynyl, imino, aryl, carbocycle, heterocycle, aralkyl, alkylaryl, alkylaryloxy, aryloxy, aralkyloxy, aralkylsulfonyl, aralkylamino, arylamino, arylazo, arylthio, aralkylthio of R1-R8, X, Y, or Z is optionally substituted with one or more substituents selected from hydroxy, halo, haloalkyl, haloalkylamide, thiocarbonyl, double-bonded oxygen to form carbonyl, carboxy, alkoxy, alkenoxy, cyano, nitro, amino, imino, amide, xe2x80x94NHCOR9 or xe2x80x94COOR9 where R9 is defined above, C1-C6 straight or branched chain alkyl, C2-C6 straight or branched chain alkenyl or alkynyl, alkylamino, aminoalkyl, sulfhydryl, thioalkyl, alkylthio, sulfonyl, aryl, aralkyl, aryloxy, arylamino, arylazo, arylthio, carbocycle, or heterocycle.
The present invention further relates to a method of inhibiting PARP activity, treating or preventing diseases or disorders, altering gene expression, or radiosensitizing, comprising: administering a therapeutically effective amount of a compound of formula I: 
or a pharmaceutically acceptable salt, hydrate, ester, solvate, prodrug, metabolite, stereoisomer, or mixtures thereof, wherein R1-R9 and Z are independently hydrogen, hydroxy, halo, haloalkyl, thiocarbonyl, cyano, nitro, amino, imino, alkylamino, aminoalkyl, sulfhydryl, thioalkyl, alkylthio, sulfonyl, alkylsulfonyl, C1-C9 straight or branched chain alkyl, C2-C9 straight or branched chain alkenyl, C2-C9 straight or branched chain alkynyl, C1-C6 straight or branched chain alkoxy, C2-C6 straight or branched chain alkenoxy, C2-C6 straight or branched chain alkynoxy, aryl, carbocycle, heterocycle, aralkyl, alkylaryl, alkylaryloxy, aryloxy, aralkyloxy, aralkylsulfonyl, aralkylamino, arylamino, arylazo, arylthio, or aralkylthio; or Z is 
wherein U is C or N, and R7 and R8 are defined above; and X and Y are independently aryl, carbocycle, or heterocycle;
wherein said alkyl, alkenyl, alkynyl, imino, aryl, carbocycle, heterocycle, aralkyl, alkylaryl, alkylaryloxy, aryloxy, aralkyloxy, aralkylsulfonyl, aralkylamino, arylamino, arylazo, arylthio, aralkylthio of R1-R8, X, Y, or Z is optionally substituted with one or more substituents selected from hydroxy, halo, haloalkyl, haloalkylamide, thiocarbonyl, double-bonded oxygen to form carbonyl, carboxy, alkoxy, alkenoxy, cyano, nitro, amino, imino, amide, xe2x80x94NHCOR9 or xe2x80x94COOR9 where R9 is defined above, C1-C6 straight or branched chain alkyl, C2-C6 straight or branched chain alkenyl or alkynyl, alkylamino, aminoalkyl, sulfhydryl, thioalkyl, alkylthio, sulfonyl, aryl, aralkyl, aryloxy, arylamino, arylazo, arylthio, carbocycle, or heterocycle.